Habitat influences on sea urchin populations.

This study determined the extent of variation in sea urchin populations in different habitats. Study areas, each with varying amounts of algal cover, were monitored seasonally for one year at Shemya Island, Alaska, for algal cover and drift algae. Habitat types were characterized as either dense kelp beds, sparse kelp beds, or barrens grounds (low to no foliose algal cover). Within each habitat, urchin density, size, gonad and nutrition indices, and mobility were monitored. In general, algal drift was more abundant in the high kelp areas; however, abundances of drift varied by time of year and water depth. Urchin density, size, gonad index, and mobility also varied by time of year, macro algal cover, and depth. Urchin nutrition index followed no discernible pattern. This study showed that certain parameters of urchin populations are strongly influenced by habitat type and time of year.